This invention relates to a method for measuring itch sensitivity consistently and accurately so that antipruritic products for alleviating itch can be evaluated. This invention further relates to an apparatus for the measurement of tactile sensation which includes multiple-head monofilaments configured to make the monofilaments readily accessible for rapid use while at the same time protecting the monofilaments from damage.
The Semmes-Weinstein Pressure Aesthesiometer is a well known device to measure tactile thresholds. It comprises a set of several plastic filaments of constant length with various diameters that apply differing maximal forces across the different filaments. Such a conventional esthesiometer is useful for the measurement of skin irritations, but due to the presence of sharp edges on the tips of the filaments, this conventional esthesiometer causes pain and twisting errors which reduce measuring accuracy and which preclude its application to various measurements including itch sensation.
A procedure for measuring itch sensation has been described by applicant Sidney Weinstein in a report to Alcon Laboratories entitled "Comparison of Three Antipruritics and A Vehicle", dated Apr. 29, 1980. Monofilaments are used to produce itch by means of dragging a specified monofilament across the skin at a 45 degree angle. The characteristic force and length of the specific monofilament cause it to produce a distinctive itch for a particular person, as people have different thresholds for itch. The force applied by the monofilament is determined basically by the physical dimensions of the monofilament; each monofilament as applied to the skin surface applies an increasing force as it is bent, but once bent, applies a characteristic calibrated force (within a percentage error). If increasing force is applied, the monofilament bends without applying additional downward force to the test site. If further force is applied, the monofilament eventually kinks destructively or the contacting surface unintentionally slips off the surface of the subject skin test site.
This known itch measurement procedure relied upon the then existing Semmes-Weinstein Pressure Aesthesiometer, which rendered the measurements very unreliable due to the problems of twisting, breaking and slipping of the monofilament, and moreover, because the inducing procedure scratched a subject skin surface so as to alleviate itch while trying to measure same. Therefore, this prior procedure did not allow for the precise determination of functional relationships between antipruritics.
The conventional filament kit having a number of individual monofilaments, moreover, is cumbersome to carry, time consuming to use, and prone to damage. Typically, a handle is provided to which filaments of various diameters can be permanently attached or removably attached, one-by-one, to perform testing. While in a "storage configuration" the filaments are safe from breakage but are inaccessible and difficult to use rapidly. A device having a handle which includes multiple heads for simultaneously holding multiple filaments has been proposed by Judith Bell-Krotoski in the Journal of Hand Therapy, "Pocket Filaments and Specifications for the Semmes-Weinstein Monofilaments" (January-March 1990). The Bell-Krotoski holder, however, exposes the filaments to damage and breakage during use and storage.
Application Ser. No. 07/860,900 discloses an esthesiometer having a stable, functional easy to manufacture tip which better engages the skin of a subject and which overcomes the problems of pain errors and twisting errors. The apparatus disclosed therein comprises a set of unitarily formed monofilaments whose tips are textured and curved. The unitary tip of the monofilaments disclosed in application Ser. No. 07/860,900 accordingly does not break or fall off, and due to its texture and curvature is accordingly capable of eliciting tactile pressure stimulations that are more consistently of the pressure type and that are more accurately recordable than the conventional esthesiometer, which elicits both pressure and pain stimulations randomly.